1. Field of the Invention
The present invention relates to an inkjet printing apparatus, and more particularly to technology for improving positional deviation between front and rear surface images produced by double-side printing.
2. Description of the Related Art
When performing double-side printing by an offset printing machine using a printing plate, normally, after printing on a front surface with trim marks, the paper is inverted and the rear surface printing is carried out, whereupon an operator looks through the resulting output printed object, or performs an inspection by passing a needle therethrough, and the tension of printing plate is adjusted, and the like, on the basis of the inspection results, so as to align the positions of the rear and front surfaces. In the case of an offset printer, since there is a small amount of water in the ink compared to aqueous inkjet printing, then there has been virtually no problem of deformation of the paper due to expansion and contraction in relation to the image density (ink volume).
On the other hand, with an inkjet printer which uses water-soluble ink, there is a large amount of water contained in the ink, and therefore the paper expands and contracts, depending on the ink volume (image density) adhering to the paper, and the difference between the front and rear surface positions in the printed image on the rear surface (positional deviation between the front and rear images) becomes large, which is a disadvantage compared to the offset printing.
In respect of image position alignment technology, Japanese Patent Application Publication No. 2009-279821 discloses a line type inkjet printing apparatus which detects deviation in the paper width direction caused by the previous printing operation, by means of a paper position sensor, and moves the position of image data. Japanese Patent Application Publication No. 2010-12757 discloses a printer apparatus in which a reference mark is also printed when printing on the front surface, the reference mark on the rear side surface (printed surface) are detected when printing on the rear surface, and the printing position of image data for rear surface printing is corrected. Furthermore, Japanese Patent Application Publication No. 2002-236015, Japanese Patent Application Publication No. 2001-146006, Japanese Patent Application Publication No. 11-315484 and Japanese Patent Application Publication No. 10-166566 each disclose a method in which a reference image mark is formed in advance and printing is performed from both the front and rear surfaces so as to be aligned with the reference image mark.
However, in the case of aqueous inkjet printing, there is great deformation of the paper dimensions, depending on the storage time and storage environment after printing on the front surface (first surface), and there has been no simple method for aligning the image positions on the front and rear surface images, which is appropriate in respect of paper deformation of this kind.
Furthermore, in a method which records a reference mark only on a front surface, as proposed in the related art, the accuracy of measurement of the amount of deformation of the paper is limited by the resolution of the imaging system which determines the amount of deformation.